I wouldn't switch back and forth just because it could cause stomach issues such as constipation. Their little bodies cant handle change like that constantly. Maybe try to find a generic brand of the enfamil formula. Just read all the ingredients and compare the two. I've been using Gerber soothe for my two week old but it's $26 a container and we can't afford that. So we found out that the CVS brand is the same exact thing but only $16 a container. So try to compare formula and find one that'stthe same as enfamil. I know that the brand parents choice is really similar to enfamil. I don't use it though because the main ingredient is corn syrup.
The doctor will more than likely tell you to only use one kind of formula, but when my daughter was little, WIC gave her enfamil and when we would run out of that, id get her the parents choice kind from walmart. I also had similac they gave me at the hospital and i used that with no problems. She never had any issues switching between brands. Your the mommy and you know your baby best so if you think she can handle it, im sure itll be just fine.
Ask her dr. I never formula fed but ive always been under the impression that youre only supposed to use one kind of formula to reduce the risk of allergies or tummy problems